Mercury pollution is of growing global concern due to the widespread atmospheric transport of gaseous mercury species and its biological toxicity. After being scavenged from the atmosphere, inorganic mercury (Hg2+) is methylated in anoxic zones of aquatic and terrestrial ecosystems to form organomercurial compounds, including monomethylmercury. Unlike inorganic mercury, the high biological transfer efficiency of organomercurial compounds allows them to biomagnify in a similar fashion to organic compounds. Biomagnification is the ability of a species to build up to high levels in the microscopic animals, fish, and fish consumers that make up aquatic and terrestrial food webs. The significant difference between the toxicity of organomercurial compounds and inorganic mercury makes the analytical methods for distinguishing these different mercury species critical for both research and environmental monitoring purposes.
For example, in the decade since the development of the aqueous [ethylation/gas chromatography (GC)/atomic fluorescence spectrometry (AFS)] analysis method was developed, our understanding of the biochemistry of monomethylmercury has increased. This method, however, is difficult and time consuming, which limits its use. Despite the previous progress with the [ethylation/GC/AFS] method, there is a need for more rapid analytical methods to reduce the difficulty and cost of measuring monomethylmercury at environmental concentrations.
Existing high-pressure liquid chromatography (HPLC) based systems for separation and quantification of inorganic and monomethylmercury have failed to overcome the key obstacles inherent in environmental mercury analysis: trace-level detection and matrix interferents. Due to the very low, or trace-level, amounts of mercury in the environment, analytical methods must be very sensitive. Additionally, they must retain this sensitivity in the presence of matrix interferents, which are common in lakes, streams, rivers, cell cultures, experimental media, tissue digestates, and sediment extractions.
Matrix interferents include organic molecules of natural or synthetic origin. Organic molecules of natural origin include inorganic and organic byproducts of microbial metabolism, such as sulfide and thiosulfate, products of plant and animal death and decay, such as humic acid and organic acids functionalized with thiol groups, and iron oxide colloids. Interferents of synthetic origin include EDTA, NTA, amines, amino acids, and thiosulfate.
In particular, the reduced sulfur sites present in many matrix interferents form very strong bonds with mercury. This effect can prevent monomethylmercury from being directly analyzed without complex distillation or solvent extraction from water with high interferent content.
While reverse-phase HPLC methods can separate hydrophobic 2:1 and 1:1 mercury complexes formed from ligands, such as dithiocarbamates or cysteine, current preconcentration methods coupled with HPLC are not effective at the trace mercury levels present in many environmental samples. More importantly, none of these methods can analyze for both inorganic and monomethylmercury, when significant organic and/or sulfide interferents are present in the sample. The current invention overcomes at least one of the disadvantages associated with prior analysis methods.